Count locked pages that don't need vacuuming as scanned.

Previously, if VACUUM skipped vacuuming a page because it's pinned, it
didn't count that page as scanned. However, that meant that relfrozenxid
was not bumped up either, which prevented anti-wraparound vacuum from
doing its job.

Report by Миша Тюрин, analysis and patch by Sergey Burladyn and Jeff Janes.
Backpatch to 9.2, where the skip-locked-pages behavior was introduced.
Use cstring_to_text_with_len when length is known.

This avoids a potentially-expensive extra call to strlen().

David Rowley
Replace appendPQExpBuffer(..., <constant>) with appendPQExpBufferStr

Arguably makes the code a bit more readable, and might give a small
performance gain.

David Rowley
Spell SQL keywords in uppercase in pg_dump's query.

The server won't care, but let's be consistent.

David Rowley.
unaccent:  Revert patch 9299f6179838cef8aa1123f6fb76f0d3d6f2decc

The reverted patch to change functions from strict to immutable was
incorrect and needs additional research.